Concentric Tube Heat Exchanger and Method

ABSTRACT

A heat exchanger comprises an outer tube and an inner tube. The outer tube has an annular wall and ribs. The ribs extend radially inward from the annular wall. Some of the ribs extend clockwise as they extend toward the centroid and some other of the ribs extend counter-clockwise as they extend toward the centroid. The annular wall of the inner tube has an outer surface that is in contact with the ribs of the outer tube. The outer tube and the inner tube collectively define a plurality of outer fluid passageways bound by the annular walls of the outer and inner tubes and the ribs of the outer tube. A method of assembly for terminating the outer tube of a concentric tube heat exchanger is also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to concentric tube heat exchangers comprising two separately formed concentric tubes. The invention also pertains to methods of terminating the ends of the outer tube.

2. General Background

Concentric tube heat exchangers are used in particular situations where their configuration is advantageous. For example, concentric tube heat exchangers are useful in situations involving high pressures in view of the ability of tubes to withstand high internal pressures via hoop stress. Concentric tube heat exchangers also tend to be robust. For these reasons, internal heat exchangers (IHX) of the type used in vehicular air conditioning systems to transfer heat directly from the high pressure to the low pressure refrigerant lines are often concentric tube heat exchangers.

SUMMARY OF THE INVENTION

In one aspect of the invention, a heat exchanger comprises an outer tube and an inner tube. The outer tube has an annular wall, ribs, and a transverse cross-section. The cross-section of the outer tube has a centroid and the outer tube extends along a longitudinal path. The ribs extend toward the centroid from the annular wall. Some of the ribs extend clockwise as they extend toward the centroid and some other of the ribs extend counter-clockwise as they extend toward the centroid. The inner tube has an annular wall and the outer tube encircles the inner tube. The annular wall of the inner tube has an outer surface that is in contact with at least some of the ribs of the outer tube. The inner tube encircles an inner fluid passageway that extends along the longitudinal path. The outer tube and the inner tube collectively define a plurality of outer fluid passageways bound by the annular walls of the outer and inner tubes and the ribs of the outer tube. The outer fluid passageways extend along the longitudinal path.

In another aspect of the invention, a heat exchanger comprises an outer tube and an inner tube. The outer tube has an annular wall, ribs, and a transverse cross-section. The cross-section of the outer tube has a centroid and the outer tube extends along a longitudinal path. The ribs extend toward the centroid from the annular wall of the outer tube. The annular wall of the outer tube having a longitudinal end, an enlarged region, and an opening. The opening extends through the annular wall of the outer tube within the enlarged region. The outer tube encircles the inner tube, which also has an annular wall. The annular wall of the inner tube has an outer surface that is in contact with at least some of the ribs of the outer tube. The inner tube encircles an inner fluid passageway that extends along the longitudinal path. The outer tube and the inner tube collectively define a plurality of outer fluid passageways bound by the annular walls of the outer and inner tubes and the ribs of the outer tube. The outer fluid passageways extend along the longitudinal path and are in fluid communication with the opening of the outer tube. The annular wall of the outer tube is annularly sealed to the annular wall of the inner tube at its longitudinal end.

In still another aspect of the invention, a method of forming a heat exchanger comprises expanding an outer tube. The outer tube has an annular wall, ribs, and a transverse cross-section. The cross-section of the outer tube has a centroid and the outer tube extends along a longitudinal path. The ribs extend toward the centroid from the annular wall. The annular wall of the outer tube also has a longitudinal end and the expanding causes the annular wall of the outer tube to radially expand and defines an enlarged region of the outer tube. The method further comprises forming an opening through the annular wall of the outer tube within the enlarged region and inserting an inner tube into the outer tube in a manner such that the inner tube extends through the longitudinal end of the outer tube. The inner tube has an annular wall that encircles an inner fluid passageway that extends along the longitudinal path. The insertion causes the annular wall of the inner tube to be in contact with at least some of the ribs of the outer tube in a manner that defines a plurality of outer fluid passageways that are bound by the annular walls of the outer and inner tubes and the ribs of the outer tube and in a manner such that the outer fluid passageways are in fluid communication with the opening of the outer tube. Still further, the method comprises annularly sealing the longitudinal end of the annular wall of the outer tube to the annular wall of the inner tube.

Further features and advantages of the present invention, as well as the operation of the invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of an inner tube of a concentric tube heat exchanger in accordance with the invention.

FIG. 2 depicts an embodiment outer tube that is configured to encircle the inner tube shown in FIG. 1.

FIG. 3 depicts a partial section view of the outer tube with its end expanded.

FIG. 4 depicts a partial section view similar to FIG. 3 except with the inner tube extending through the outer tube.

FIG. 5 depicts a partial section view of a heat exchanger assembly in accordance with the invention prior to being sealed.

FIG. 6 depicts the assembly shown in FIG. 5 after the outer tube has been sealed to the inner tube.

FIG. 7 depicts an alternative embodiment of an inner tube of a heat exchanger in accordance with the invention.

FIG. 8 depicts an alternative method of sealing the end of the outer tube of a concentric tube heat exchanger in accordance with the invention.

Reference numerals in the written specification and in the drawing figures indicate corresponding items.

DETAILED DESCRIPTION

FIG. 6 shows a partial section view of an embodiment of a portion of a concentric tube heat exchanger 10 in accordance with the invention. The heat exchanger 10 comprises an inner tube 12 and outer tube 14. The outer tube is sealed 14 to the inner tube 12 at its longitudinal end and an outlet tube 16 is attached to the outer tube 14 to channel fluid into or out of the outer tube. Preferably, the components of the heat exchanger 10 are formed of aluminium alloy.

The inner tube 12 can be standard smooth walled round or otherwise shaped tubing, but preferably comprises an annular wall 18 and a plurality of circumferentially spaced ribs 20 that extend radially inward from the annular wall. As shown in FIG. 1, the ribs 20 can extend longitudinally parallel to the longitudinal path of the inner tube 12. Alternatively, as shown in FIG. 7, the ribs 20′ may spiral longitudinally about the longitudinal path of the inner tube 12′. It should also be appreciated from FIGS. 1 and 7 that the ribs may be more teeth-like or alternatively more wave-like in transverse cross-section. The ribs 20 provide the inner surface of the inner tube 12 with greater surface area and may cause greater turbulence in fluid moving through the inner tube, both of which provide greater heat transfer rates.

The outer tube 14 also comprises annular wall 22 and a plurality of circumferentially spaced ribs 24 that extend radially inward from the annular wall. Preferably, the ribs 24 extend radially inward to an extent such that the ribs can contact the outer surface of the annular wall 18 of the inner tube 12, but such that the inner tube can slide relative to the outer tube with little friction. Thus, the outer tube 14 and the inner tube 12 collectively define a plurality of outer fluid passageways 26 (FIGS. 5 and 6) bound by the annular walls 18, 22 of the outer and inner tubes and the ribs 24 of the outer tube that extend along the longitudinal path of the heat exchanger 10. As shown in FIG. 2, some of the ribs 24 are skewed such that they extend clockwise as they extend toward the centroid of the outer tube 14 and some other of the ribs extending counter-clockwise as they extend toward the centroid. The skewed nature of the ribs 24 provides the ribs with greater surface area than they would otherwise have. Additionally, by skewing some to the ribs 24 clockwise and some other of the ribs counter-clockwise, as opposed to all in the same direction, the ribs are less likely to collapse against annular wall 22 of the outer tube 14 when the inner tube 12 and the outer tube rotate relative to each other. This is especially helpful in preventing such collapse when the longitudinal path of the heat exchanger 10 includes bends and the inner and outer tubes 12, 14 must be bent when assembled to each other. Like the ribs 20 of the inner tube 12, the ribs 24 of the outer tube 14 could spiral longitudinally about the longitudinal path of the outer tube and could be more teeth-like or alternatively more wave-like in transverse cross-section.

FIGS. 3 through 6 show one method of terminating the outer tube 14 of the heat exchanger 10. As shown in FIG. 3, the outer tube 14 is enlarged adjacent its longitudinal end 28, preferably via a mandrel such that, when the inner tube 12 is inserted in the outer tube 14, the ribs 24 in the enlarged region of the outer tube are radially spaced from the outer surface of the inner tube. This also radially compresses the ribs 24 of the outer tube 14 in the enlarged region. An outlet opening 30 is preferably also formed through the annular wall 22 of the outer tube 14 in the enlarged region. The inner tube 12 is inserted in the outer 14 such that the inner tube extends through the opening at the longitudinal end 28 of the outer tube. Because the ribs 24 in the enlarged region of the outer tube 14 are radially spaced from the outer surface of the inner tube 12, all of the outer fluid passageways 26 are in fluid communication with the outlet opening 30. After initially enlarging the longitudinal end 26 of the outer tube 14 the longitudinal end is preferably then crimped radially inward such that the ribs 24 of the outer tube will contact the inner tube 12. Of course, substantially the same configuration could alternatively be achieved via a single step of hydroforming the outer tube 12.

With the inner tube 12 extending through the longitudinal end 28 of the outer tube 14, the longitudinal end is preferably sealed to annular wall 18 of the inner tube by soldering, brazing or welding. The solder, braze or weld is shown in FIG. 6 at reference numeral 32. Of course, an adhesive can also be used. The outlet tube 16 is attached to the outlet opening 30, optionally via a fitting 36, and preferably using said soldering, brazing or welding technique (not shown). As such, fluid can be pumped into or out of the outer fluid passageways 26 of the heat exchanger via the outlet tube 16. Obviously, the other end of the outer tube 14 preferably terminates in a similar manner.

An alternative way of terminating the ends of the outer tube 14 is shown in FIG. 8 that uses a termination fitting 38. Using the termination fitting 38, enlargement of the outer tube 14 adjacent its longitudinal end 28 isn't needed, nor is the formation of an outlet opening 30 though the annular wall of the outer tube. Instead, the termination fitting 38 provides an annular gap 40 encircling the inner tube 12 that is in fluid communication with the outer fluid passageways 26, and comprises an outlet opening 42 that is connectable to an outlet tube 16. The termination fitting 38 can be attached to the inner tube 12, the outer tube 14, and the outlet tube 16 via soldering, brazing, or welding. Alternatively, adhesive may be used.

In view of the foregoing, it should be appreciated that the invention has several advantages over the prior art. For example, the invention provides for an efficient concentric tube heat exchanger that is relatively easy to form and that can easily be bent into a desired shape without collapsing the annular walls of the inner and outer tubes against each other.

As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. For example, although the embodiment of the invention described above is a ball valve, the invention is not limited to ball valves and is equally applicable to other valves such as butterfly valves. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

It should also be understood that when introducing elements of the present invention in the claims or in the above description of exemplary embodiments of the invention, the terms “comprising,” “including,” and “having” are intended to be open-ended and mean that there may be additional elements other than the listed elements.

Additionally, the term “portion” should be construed as meaning some or all of the item or element that it qualifies. Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed, unless such an order is inherent. 

What is claimed is:
 1. A heat exchanger comprising: an outer tube having an annular wall, ribs, and a transverse cross-section, the cross-section of the outer tube having a centroid, the outer tube extending along a longitudinal path, the ribs extending toward the centroid from the annular wall of the outer tube, some of the ribs extending clockwise as they extend toward the centroid and some other of the ribs extending counter-clockwise as they extend toward the centroid; and an inner tube having an annular wall, the outer tube encircling the inner tube, the annular wall of the inner tube having an outer surface, the outer surface being in contact with at least some of the ribs of the outer tube, the inner tube encircling an inner fluid passageway that extends along the longitudinal path, the outer tube and the inner tube collectively defining a plurality of outer fluid passageways bound by the annular walls of the outer and inner tubes and the ribs of the outer tube, the outer fluid passageways extending along the longitudinal path.
 2. A heat exchanger in accordance with claim 1 wherein the ribs of the outer tube consist only of the ribs that extend clockwise and the ribs that extend counter-clockwise, and the ribs that extend clockwise alternate with the ribs that extend counter-clockwise.
 3. A heat exchanger in accordance with claim 1 wherein the inner tube comprises ribs, the ribs extending toward the centroid from the annular wall of the inner tube.
 4. A heat exchanger in accordance with claim 3 wherein the ribs of the inner tube spiral about the longitudinal path.
 5. A heat exchanger in accordance with claim 1 wherein the outer tube comprises a longitudinal end and the heat exchanger further comprises an end fitting connected to the longitudinal end, the end fitting having a primary opening through which the inner tube extends, the end fitting having a secondary opening that is in fluid communication with the outer fluid passageways.
 6. A heat exchanger in accordance with claim 1 wherein the longitudinal path is linear, the ribs of the outer tube extend parallel to the longitudinal path, and the annular walls of the inner and outer tubes are cylindrical.
 7. A heat exchanger comprising: an outer tube having an annular wall, ribs, and a transverse cross-section, the cross-section of the outer tube having a centroid, the outer tube extending along a longitudinal path, the ribs extending toward the centroid from the annular wall of the outer tube, the annular wall of the outer tube having a longitudinal end, an enlarged region, and an opening, the opening extending through the annular wall of the outer tube within the enlarged region; and an inner tube having an annular wall, the outer tube encircling the inner tube, the annular wall of the inner tube having an outer surface, the outer surface being in contact with at least some of the ribs of the outer tube, the inner tube encircling an inner fluid passageway that extends along the longitudinal path, the outer tube and the inner tube collectively defining a plurality of outer fluid passageways bound by the annular walls of the outer and inner tubes and the ribs of the outer tube, the outer fluid passageways extending along the longitudinal path and being in fluid communication with the opening of the outer tube, the annular wall of the outer tube being annularly sealed to the annular wall of the inner tube at the longitudinal end.
 8. A heat exchanger in accordance with claim 7 wherein the inner tube extends through and beyond the longitudinal end of the annular wall of the outer tube.
 9. A heat exchanger in accordance with claim 7 wherein the ribs extend within the enlarged region of the outer tube and are spaced radially from the outer surface of the annular wall of the inner tube within the enlarged region.
 10. A heat exchanger in accordance with claim 7 wherein some of the ribs extend clockwise as they extend toward the centroid and some other of the ribs extend counter-clockwise as they extend toward the centroid.
 11. A heat exchanger in accordance with claim 7 wherein the inner tube comprises ribs that extend toward the centroid from the annular wall of the inner tube.
 12. A heat exchanger in accordance with claim 11 wherein the ribs of the inner tube spiral about the longitudinal path.
 13. A heat exchanger in accordance with claim 7 wherein the annular wall of the outer tube is annularly sealed to the annular wall of the inner tube via solder, a braze, or a weld.
 14. A heat exchanger in accordance with claim 7 further comprising an outlet tube extending external to the outer tube and connected to the opening of the outer tube, the outlet tube having an internal passageway that is in fluid communication with the outer fluid passageways.
 15. A heat exchanger in accordance with claim 7 wherein the annular wall of the outer tube comprises a crimped region adjacent the longitudinal end of the annular wall of the outer tube and is annularly sealed to annular wall of the inner tube via solder, a braze, or a weld at the crimped region.
 16. A method of forming a heat exchanger comprising: expanding an outer tube, the outer tube having an annular wall, ribs, and a transverse cross-section, the cross-section of the outer tube having a centroid, the outer tube extending along a longitudinal path, the ribs extending toward the centroid from the annular wall of the outer tube, the annular wall of the outer tube having a longitudinal end and the expanding of the outer tube causing the annular wall of the outer tube to radially expand and defining an enlarged region of the outer tube; forming an opening through the annular wall of the outer tube within the enlarged region; inserting an inner tube into the outer tube in a manner such that the inner tube extends through the longitudinal end of the outer tube, the inner tube having an annular wall that encircles an inner fluid passageway that extends along the longitudinal path, the insertion causing the annular wall of the inner tube to be in contact with at least some of the ribs of the outer tube in a manner defining a plurality of outer fluid passageways bound by the annular walls of the outer and inner tubes and the ribs of the outer tube and in manner such that the outer fluid passageways are in fluid communication with the opening of the outer tube; and annularly sealing the longitudinal end of the annular wall of the outer tube to the annular wall of the inner tube.
 17. A method in accordance with claim 16 wherein the enlarged region of the outer tube comprises portions of the ribs and the expanding of the outer tube occurs in a manner that causes the ribs of the outer tube to radially move away from the centroid within the enlarged region.
 18. A method in accordance with claim 16 wherein the method further comprises crimping the annular wall of the outer tube adjacent the longitudinal end of the annular wall of the outer tube.
 19. A method in accordance with claim 18 wherein the sealing of the longitudinal end of the annular wall of the outer tube to the annular wall of the inner tube comprises soldering, brazing, or welding.
 20. A method in accordance with claim 16 wherein the method further comprises connecting an outlet tube to the opening of the outer tube, the outlet tube has an internal passageway and extends external to the outer tube, and the connecting of the outlet tube occurs in a manner such that the internal passageway of the outlet tube is in fluid communication with the outer fluid passageways. 